The present disclosure is directed to polymeric beads, methods of making the beads, and methods of using the beads as high-capacity anion exchange materials. In particular, the disclosure provides polymeric beads comprising a cross-linked polyamine and having a crush strength of about 250 g/bead or more. Preferably, the beads are substantially spherical. Also disclosed are polymeric beads comprising a cross-linked polyamine that has a substantial number of both strong base sites and weak base sites. Methods of using the polymeric beads in various industrial applications to remove or collect an unwanted or target ion, such as groundwater remediation, radio waste management, municipal wastewater management, demineralization, toxin removal, mining, food refinery, research, agriculture, and the like, are also disclosed herein.
Anion exchange resins are widely used in industry to remove or trap unwanted or target anions from an aqueous medium. Currently, commercial anion exchange resins are primarily made out of cross-linked styrene-divinyl benzene and acrylic type polymers, whose capacity are limited by their inherent low nitrogen content (e.g., 1.4 eq/L for a strong base resin and 2.0 eq/L for a weak base resin). It is desirable to obtain high-capacity resins for improving existing applications and that hold promise for use in new applications.
High capacity materials have been previously disclosed (see, e.g., U.S. Pat. No. 3,210,299) and are commercially available (e.g., Purolite® S106 and Resintech® SIR-700), but such high capacity materials have not been disclosed in bead form. Bead morphology plays an important role in many ion exchange applications. In particular, mechanical abrasion and compression during use can put pressure on a bead, and result in bead deformation, fracture, chipping, and/or crushing. This is particularly problematic for beads that do not have a spherical morphology, as edges of the beads are more susceptible to chipping and fracture. In addition, a spherical bead morphology better reduces the pressure drop, and resists osmotic pressure, during repetitive expansions and contractions that occur during bead use, and produces a better elution profile, and thus better separation, than irregularly shaped materials. It is thus desirable for an ion exchange bead to be as close to spherical as possible.
In order to be better suited for use in industrial or commercial-scale water treatment or ion exchange applications, it is also important for the crush strength of the bead to be sufficiently high, such that the bead does not deform, chip, or crush under pressures common in these applications. Although some have reported the preparation of polymeric beads made from high density nitrogen oligomers or polymers with various cross-linkers in an inverse suspension process (see, e.g., U.S. Pat. Nos. 3,803,237 and 7,459,502, as well as articles by Diallo, et al., Environmental Science and Technology, 46 (19). pp. 10718-10726, and Environmental Science and Technology, 46 (16). pp. 8998-9004), the compositions disclosed or prepared therein do not possess a crush strength sufficiently high to be suitable for use in such industrial applications. Thus, there continues to be a need to develop high-capacity, ion exchange materials that meet these industrial mechanical strength requirements.